1. Field of the Invention
This invention relates to a magnetic transfer apparatus for transferring information to a magnetic recording medium (slave medium) from a master information carrier carrying thereon a magnetic layer pattern representing the information to be transferred to the magnetic recording medium.
2. Description of the Related Art
With an increase in information quantity, there is a demand for a magnetic recording medium which is high in capacity, low in cost and preferably requires a short time to read out a necessary part of data (a magnetic recording medium which allows so-called high-speed access). As an example of such a magnetic recording medium, there has been known a high recording density magnetic medium such as a hard disc or a flexible disc. To realize the high capacity, so-called servo tracking technology for causing a magnetic head to accurately trace narrow data tracks plays an important role. To perform the servo tracking, a servo tracking signal, an address information signal, a reproduction clock signal and the like are recorded on the disc at certain intervals as so-called preformat.
As a method of recording the preformat accurately and efficiently, there has been proposed, for instance, in Japanese Unexamined Patent Publication No. 63(1988)-183623 and U.S. Pat. No. 6,347,016, a magnetic transfer method in which a pattern which is formed on a master information carrier and represents servo information is copied to a magnetic recording medium (a slave medium) by magnetic transfer.
In the magnetic transfer, a master information carrier having thereon an irregularity pattern (a pattern of protruding portions and recessed portions) representing information (e.g., servo information) to be transferred to a slave medium (a magnetic recording medium such as a magnetic disc) and a magnetic layer formed at least on the protruding portions is brought into a close contact with the slave medium and a transfer magnetic field is applied to the master information carrier and the slave medium in a close contact with each other, whereby a magnetization pattern corresponding to the information represented by the irregularity pattern is magnetically transferred from the master information carrier to the slave medium. Accordingly, the information carried by the master information carrier can be statically recorded on the slave medium with the relative position between the master information carrier and the slave medium kept constant. Thus, according to the magnetic transfer, the preformat recording can be performed accurately and the time required for the preformat recording is very short.
We, this applicant, have proposed in Japanese Unexamined Patent Publication No. 2001-14667 a method of magnetic transfer in which the magnetic layer of the slave medium is initially magnetized in one direction of the recording tracks and a transfer magnetic layer is applied to the slave medium in the direction opposite to the direction of the initial-magnetization with the slave medium held in close contact with the master information carrier. By this method, a very good magnetic transfer can be effected.
An optimal intensity of the transfer magnetic field is substantially the same as the coercive force Hc of the slave medium and an optimal intensity of the initial DC magnetic field is about twice the coercive force Hc of the slave medium.
As a method of applying the initial DC magnetic field or the transfer magnetic field to the slave medium, a method in which a local magnetic field is generated in an area of the recording track in a tangential direction of the track and a magnetic field is applied over the entire area of the track by rotating the slave medium relatively to the local magnetic field can be considered. Since the magnetic field in a tangential direction of the track is in parallel to the track at the point of contact between the track and the tangent, it is considered that a magnetic field can be applied over the entire area of the track by rotating the slave medium relatively to the local magnetic field. However, since a magnetic field actually generated by a magnetic field generating means has certain spread in a tangential direction, an area of the track deviated from the point of contact between the track and the tangent undergoes a magnetic field in a direction deviated from the direction of the track. When the intensity of a magnetic field in a direction deviated from the direction of the track is strong, the initial magnetization pattern or the transfer magnetization pattern of the area subjected to the magnetic field is disturbed and the magnetic transfer cannot be accurate. In the case where the signal to be transferred is a servo signal, satisfactory tracking function cannot be obtained on the slave medium, which deteriorates the reliability of the slave medium.